1. Field of the Invention
This invention relates generally to an RF electrode apparatus used in the treatment of tumors and, more particularly, to a coiled RF electrode apparatus that surrounds a volume of a tissue target for desiccation of the tissue and provides both ablation and hyperthermia treatment of the tumor.
2. Description of the Related Art
Current open procedures for treatment of tumors are extremely disruptive and cause a great deal of damage to healthy tissue. Accordingly, there has recently been a fair amount of emphasis on minimally invasive procedures for tissue destruction and removal.
It is known that elevating the temperature of tumors is helpful in the treatment and management of cancerous tissues. The mechanisms of selective cancer cell eradication by hyperthermia is not completely understood. However, four cellular effects of hyperthermia on cancerous tissue have been proposed, (i) changes in cell or nuclear membrane permeability or fluidity, (ii) cytoplasmic lysomal disintegration, causing release of digestive enzymes, (iii) protein thermal damage affecting cell respiration and the synthesis of DNA and RNA and (iv) potential excitation of immunologic systems. Treatment methods for applying heat to tumors include the use of direct contact radio-frequency (RF) applicators, microwave radiation, inductively coupled RF fields, ultrasound, and a variety of simple thermal conduction techniques.
Among the problems associated with all of these procedures is the requirement that highly localized heat be produced at depths of several centimeters beneath the surface of the body. Certain techniques have been developed with microwave radiation and ultrasound to focus energy at various desired depths. RF applications may be used at depth during surgery. However, the extent of localization is generally poor with the result that healthy tissue may be harmed. Induction heating gives rise to poor localization of the incident energy as well. Although induction heating may be achieved by placing an antenna on the surface of the body, superficial eddy currents are generated in the immediate vicinity of the antenna when it is driven using RF current, and unwanted surface heating occurs with little coupled to the underlying tissue. Thus, non-invasive procedures for providing heat to internal tumors have had difficulties in achieving substantial specific and selective treatment.
Hyperthermia, which can be from an RF or microwave source, applies heat to tissue but does not exceed 45 degrees C. so that normal cells survive. In thermotherapy, heat energy of greater than 45 degrees C. is applied, resulting in histological damage and the denaturalization of proteins. Hyperthermia has been applied more recently for therapy of malignant tumors. In hyperthermia, it is desirable to induce a state of hyperthermia that is localized by interstitial current heating to a specific area while concurrently insuring minimum thermal damage to healthy surrounding tissue. Often, the tumor is located subcutaneously and addressing the tumor requires either surgery, endoscopic procedures or external radiation. It is difficult to externally induce hyperthermia in deep body tissue because current density is diluted due to its absorption by healthy tissue. Additionally, a portion of the RF energy is reflected at the muscle/fat and bone interfaces which adds to the problem of depositing a known quantity of energy directly on a small tumor.
Attempts to use interstitial local hyperthermia have not proven to be very successful. Results have often produced nonuniform temperatures throughout the tumor. It is believed that tumor mass reduction by hyperthermia is related to thermal dose. Thermal dose is the minimum effective temperature applied throughout the tumor mass for a defined period of time. Because blood flow is the major mechanism of heat loss for tumors being heated, and blood flow varies throughout the tumor, more even heating of tumor tissue is needed to ensure effective treatment.
The same is true for ablation of the tumor itself through the use of RF energy. Different methods have been utilized for the RF ablation of masses such as tumors. Instead of heating the tumor it is ablated through the application of energy. This process has been difficult to achieve due to a variety of factors including, (i) positioning of the RF ablation electrodes to effectively ablate all of the mass, (ii) introduction of the RF ablation electrodes to the tumor site and (iii) controlled delivery and monitoring of RF energy to achieve successful ablation without damage to non-tumor tissue.
There have been a number of different treatment methods and devices for treating tumors minimally invasively. One such example is an endoscope that produces RF hyperthermia in tumors, as disclosed in U.S. Pat. No. 4,920,978. A microwave endoscope device is disclosed in U.S. Pat. No. 4,409,993.
An apparatus for hyperthermic treatment of tumors is disclosed in U.S. Pat. No. 4,846,196. Two electrodes are connected to an RF energy source. One of the electrodes is shaped with an external surface the same size as the tumor area. It is used as the treatment electrode. The other electrode is an indifferent electrode and is in external contact with the skin of the body.
In U.S. Pat. No. 4,763,671 (the "'671 patent"), a minimally invasive procedure utilizes two catheters that are inserted interstitially into the tumor. The catheter includes a hard plastic support member. Around the support member is a conductor in the form of an open mesh. A layer of insulation is secured to the conductor with adhesive beads. It covers all of the conductor except a preselected length which is not adjustable. Different size tumors can not be treated with the same electrode. The device of the '671 patent fails to provide for the introduction of a fluidic medium, such as a chemotherapeutic agent, to the tumor for improved treatment.
In U.S. Pat. No. 4,565,200 (the "'200 patent"), an electrode system is described in which a single entrance tract cannula is used to introduce an electrode into a selected body site. The device of the '200 patent fails to provide for an electrode which surrounds the tumor for ablation or hyperthermia treatment.
However, none of these devices provide for the effective treatment of a tumor with RF energy that is used to ablate the tumor, introduce energy for hyperthermia, and finally introduce a chemotherapeutic agent.
It would be desirable to provide an RF treatment device that would be capable of ablation and hyperthermia as well as introduction of chemotherapeutic agent. Additionally, it would be an advancement to provide a device that would include at least one electrode which is advanced out of the distal tip of an introducing catheter and, as it is advanced, it becomes a wound electrode which continues to travel around the periphery of the outside of the tumor until substantially most of the tumor is surrounded by the electrode.